Method and apparatus for regenerating optical signals in an all-optical cross-connect switch

ABSTRACT

Methods, apparatus and systems for regenerating, monitoring and bridging optical signals through an optical cross-connect switch to provide increased reliability. A self testing method, apparatus and system for an optical cross-connect switch. An optical-to-electrical-to-optical converter (O/E/O) is provided in an optical cross-connect switch to provide optical-electrical-optical conversion. I/O port cards having an optical-to-electrical-to-optical converter are referred to as smart port cards while I/O port cards without an optical-to-electrical-to-optical converter are referred to as passive port cards. Test port/monitor cards are also provided for testing optical cross-connect switches. Methods, apparatus and systems for performing bridging, test access, and supporting redundant optical switch fabrics are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This non-provisional U.S. Patent Application claims the benefitof U.S. Provisional Patent Application No. 60/162,936 entitled “OPTICALCROSSCONNECT WITH OPTICAL TO ELECTRICAL CONVERTERS” filed on Nov. 2,1999 by inventor Rajiv Ramaswami; and also claims the benefit of U.S.Provisional Patent Application No. 60/170,094 entitled “OPTICALCROSSCONNECT WITH BRIDGING, TEST ACCESS AND REDUNDANCY” filed on Dec.10, 1999 by inventors Rajiv Ramaswami and Robert R. Ward; and alsoclaims the benefit of U.S. Provisional Patent Application No. 60/170,095entitled “OPTICAL CROSSCONNECT WITH LOW-LOSS BRIDGING, TEST ACCESS ANDREDUNDANCY” filed on Dec. 10, 1999 by inventors Steven Clark and RajivRamaswami; and also claims the benefit of U.S. Provisional PatentApplication No. 60/170,093 entitled “1+1 OPTICAL PROTECTION USINGOPTICAL CROSSCONNECT” filed on Dec. 10, 1999 by inventors RajivRamaswami and Robert R. Ward which is incorporated herein by reference;and also claims the benefit of U.S. Provisional Patent Application No.60/170,092 entitled “SIGNALING INTERFACE BETWEEN OPTICAL CROSSCONNECTAND ATTACHED EQUIPMENT” filed on Dec. 10, 1999 by inventor RajivRamaswami; and also claims the benefit of U.S. Provisional PatentApplication No. 60/186,108 entitled “1:N PROTECTION BETWEEN CLIENTS ANDALL-OPTICAL CROSSCONNECTS” filed on Mar. 1, 2000 by inventors KentErickson, Subhashini Kaligotla, and Rajiv Ramaswami; and also claims thebenefit of U.S. Provisional Patent Application No. 60/200,425 entitled“OPTICAL CROSSCONNECT SYSTEM” filed on Apr. 28, 2000 by inventors RajivRamaswami, Steve Tabaska, and Robert Ward.

BACKGROUND OF THE INVENTION

[0002] Over the last few years, the demand for high-speed communicationnetworks has increased dramatically. In many situations, communicationnetworks are implemented with electrical interconnections. That is theinterconnections between nodes and networks are made using electroniccircuitry such as a transistor switch which blocks or passes electrons.One type of electrical interconnection is an electronic network switchwhich is well known. The application of electronic network switches tolocal area networks (LANs), metropolitan area networks (MANs) and widearea networks (WANs) is also well know. A network switch may stand aloneor be used in conjunction with or incorporated into other networkequipment at a network node. As desired levels of bandwidth andtransmission speed for communication networks increase, it will becomemore difficult for the electrical interconnections to satisfy theselevels.

[0003] One difficulty associated with electrical interconnections isthat they are sensitive to external electromagnetic interference. Morespecifically, electromagnetic fields that reside in the vicinity of theinterconnection lines induce additional currents, which may causeerroneous signaling. This requires proper shielding, which hamperedgeneral heat removal.

[0004] Another difficulty is that electrical interconnections aresubject to excessive inductive coupling, which is referred to as“crosstalk”. To alleviate crosstalk, the electrical interconnectionsmust be shielded or abide by fundamental rules of circuit routing sothat they are set at a distance large enough to prevent neighboringsignals from having any adverse effect on each other, which would reducenetwork performance.

[0005] In lieu of electrical interconnections switching electrons or avoltage and current, optical interconnections offer a solution to thedifficulties affecting conventional electrical interconnections. Opticalinterconnections switch photons or light ON and OFF at one or morewavelengths to provide signaling. An advantage to opticalinterconnections is that they are not as susceptible to inductive oreven capacitive coupling effects as electrical interconnections. Inaddition, optical interconnections offer increased bandwidth andsubstantial avoidance of electromagnetic interference. This potentialadvantage of optics becomes more important as the transmission ratesincrease and as the strength of mutual coupling associated withelectrical interconnections is proportional to the frequency of thesignals propagating over these interconnections.

[0006] Albeit local or global in nature, many communications networkfeatures electronic switching devices to arbitrate the flow ofinformation over the optical interconnections. Conventional electronicswitching devices for optical signals are designed to include hybridoptical-electrical semiconductor circuits employing photodetectors,electrical switches, optical modulator or lasers. The incoming opticalsignals are converted to electrical signals by photodetectors. Theelectrical signals are amplified and switched by electronic switches tothe appropriate output and then converted into optical signals bylasers. One disadvantage associated with a conventional electronicswitching device is that it provides less than optimal effectiveness insupporting high data transmission rates and bandwidth.

[0007] An alternative approach is to develop an optical cross-connectsystem which performs switching operations of light pulses or photons(referred to generally as “light signals”) without converting andreconverting signals between the optical domain to the electricaldomain. However, switching light or photonic signals is different andintroduces additional challenges over conventional electrical switching.One of these challenges is fault protection. Failure modes in an opticalsystem typically include a faulty component which can be catastrophicsevering a communication channel or causing periodic generation of biterrors.

[0008] Another challenge to an optical cross-connect system, isgenerating status information regarding the data transmission status ofthe light or optical signals through the optical cross-connect. Yetanother challenge in an optical cross-connect system is in creating areliable optical cross-connect switch. Still yet another challenge in anoptical cross-connect system is the ability to completely test such asystem. These are challenges because the light or optical signals arenot in an electrical form in an all optical cross-connect system and thedata format and the data rate of individual channels is unknown to anall optical cross-connect system. Each and every channel can have theirlight pulses converted into electrical pulses for monitoring but this isan expensive solution which requires an optical to electrical conversionfor each and every channel.

SUMMARY OF THE INVENTION

[0009] The present invention is briefly described in the claims thatfollow below.

[0010] Briefly, the present invention provides methods, apparatus andsystems for performing optical-electrical-optical conversion in anoptical cross-connect switch. An optical-to-electrical-to-opticalconverter (O/E/O) is provided in an optical cross-connect switch toprovide the optical-electrical-optical conversion. I/O port cards havingan optical-to-electrical-to-optical converter are referred to as smartport cards while I/O port cards without anoptical-to-electrical-to-optical converter are referred to as passiveport cards. Test port/monitor cards are also provided for testingoptical cross-connect switches. Methods, apparatus and systems forperforming bridging, test access, and supporting redundant opticalswitch fabrics are also disclosed. Methods, apparatus and systems forregenerating, monitoring and bridging optical signals through an opticalcross-connect switch to provide increased reliability are alsodisclosed. A self testing method, apparatus and system for an opticalcross-connect switch is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The features and advantages of the present invention will becomeapparent from the following detailed description of the presentinvention in which:

[0012]FIG. 1 is a simplified overview of an embodiment of an opticalcross-connect switching system.

[0013]FIG. 2 is a first exemplary embodiment of an optical cross-connectswitching system of FIG. 1.

[0014]FIG. 3 is an exemplary embodiment of the optical fiber switchmatrices forming an optical fiber switch fabric of FIG. 2.

[0015]FIG. 4 is an exemplary embodiment of mirror arrays forming anoptical fiber switch matrix of FIG. 3.

[0016]FIG. 5 is an exemplary embodiment of an I/O subsystem featuring aplurality of I/O port modules.

[0017]FIG. 6 is an exemplary embodiment of a data path for the transferof light between I/O port modules and multiple fiber optical switchfabrics of FIG. 2.

[0018]FIG. 7 is an exemplary embodiment of a control path featuring theinterconnections between the I/O port module and servo modules.

[0019]FIG. 8 is an exemplary embodiment of the I/O port module of FIGS.6 and 7 illustrating a data propagation circuit and a control circuit.

[0020]FIG. 9 is an exemplary embodiment of multiple ports of I/O modulesin communication with optical switches controlled by servo modules.

[0021]FIG. 10 is an exemplary embodiment of an I/O port configured as atest access port.

[0022]FIG. 11 is an exemplary embodiment of a servo module of theoptical cross-connect switching system of FIG. 1.

[0023]FIG. 12 is an exemplary block diagram of a redundant architectureof the optical cross-connect switching system of FIG. 1.

[0024]FIG. 13 is a block diagram illustrating an out-of-band signalinginterface between an optical cross-connect switch and attached networkequipment.

[0025]FIG. 14 is a block diagram illustrating a decentralized signalinginterface between an optical cross-connect switch and attached networkequipment.

[0026]FIG. 15 is a block diagram of an optical cross-connect switchhaving various port cards including passive port cards and smart portcards having optical-electrical-optical converters.

[0027]FIG. 16 is a block diagram of an optical cross-connect switchhaving a one and two tiered port card arrangement with smart port cardshaving optical-electrical-optical converters coupled to passive portcards.

[0028]FIG. 17 is a block diagram of an optical cross-connect switchincluding port cards providing bridging in an optical switch fabric.

[0029]FIG. 18 is a block diagram of an alternate optical cross-connectincluding port cards providing bridging in an optical switch fabric.

[0030]FIGS. 19A-19G are block diagrams of an optical cross-connectswitch including smart port cards and/or passive port cards to providebridging using a redundant optical switch fabric and testing/monitoringusing a test port/monitoring card.

[0031]FIG. 20 is a block diagram of an optical cross-connect switchincluding a test port/monitoring card to provide self-testing/monitoringof the optical switch fabrics of an optical cross-connect switch havingredundant optical switch fabrics.

[0032] Like reference numbers and designations in the drawings indicatelike elements providing similar functionality. A letter or prime after areference number designator represents another or different instance ofan element having the reference number designator.

DETAILED DESCRIPTION OF THE INVENTION

[0033] In the following detailed description of the present invention,numerous specific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances well known methods,procedures, components, and circuits have not been described in detailso as not to unnecessarily obscure aspects of the present invention.

[0034] In the following description, certain terminology is used todescribe various features of the present invention. For example, a“module” includes a substrate normally formed with any type of materialor materials upon which components can be attached such as a printedcircuit board or a daughter card for example. Examples of a “component”include an optical switch, a processing unit (e.g., Field ProgrammableGate Array “FPGA”, digital signal processor, general microprocessor,application specific integrated circuit “ASIC”, etc.), splitters and thelike. A “splitter” is an optical component that performs a bridgingoperation on an input light signal by splitting that light signal intotwo or more output light signals. Each module features one or moreinterfaces to transport information over a link. A “link” is broadlydefined as one or more physical or virtual information-carrying mediumsthat establish a communication pathway such as, for example, opticalfiber, electrical wire, cable, bus traces, wireless channels and thelike. “Information” can be voice, data, address, and/or control in anyrepresentative signaling format such as light signals (e.g., lightpulses or photons).

[0035] I. General Architectural Overview

[0036] Referring to FIG. 1, an exemplary embodiment of a simplifiedoverview of an optical cross-connect switching system 100 is shown.Herein, the optical cross-connect switching system 100 comprises threebasic units: a switch subsystem 110, a switch control subsystem 120 andan input/output (I/O) subsystem 130. In one embodiment, the modulararchitecture of the switch subsystem 110, by a method of havingreplaceable optical switch cores, provides for switch subsystemmaintenance in the event of failure within the switch subsystem 110. Itis conceivable that further modularity could be achieved by havingreplaceable subsections within, thus providing for switch matrixmaintenance in the event of failure within a switch matrix itself. Themodular architecture of both the switch control subsystem 120 and theI/O subsystem 130, each handling a small number of I/O ports in thesystem 100, provides scalability to the optical cross-connect switchingsystem 100. Thus, additional I/O ports may be subsequently added to theoptical cross-connect switching system 100 by adding or removinginput/output (I/O) port modules (described below).

[0037] The switch subsystem 110 includes optical switches for routinglight signals. In one embodiment, the optical switches forming theswitch subsystem 110 are micro-machined mirrors; however, it iscontemplated that other switch fabrics may be used such as liquidcrystal technology. The I/O subsystem 130 receives external lightsignals 140 and transfers these signals to the switch subsystem 110. Theswitch control subsystem 120 controls the configuration of the switchsubsystem 110 (e.g., mirror orientation) and performs certain monitoringfunctions. The interconnectivity between the switch subsystem 110, theswitch control subsystem 120 and the I/O subsystem 130 includesredundancy so that no equipment failures would cause completedisablement of the system 100.

[0038] Referring now to FIG. 2, a first exemplary embodiment of anoptical cross-connect switching system 100 is shown. In general, theoptical cross-connect switching system 100 is a matrix-based opticalcross-connect with associated I/O port modules. More specifically, theoptical cross-connect switching system 100 is collectively formed by aplurality of platforms 205, 206 and 207 in communication with eachother, although the implementation of the switching system 100 as asingle platform is another embodiment. Herein, each platform 205, 206and 207 includes a frame 210 (e.g., a rack) that physically supports I/Oport modules forming the I/O subsystem 130 as well as servo modules,servo control modules and/or network control modules of the switchcontrol subsystem 120. The modules are arranged either horizontally orvertically within each platform 205, 206 and 207 and can be individuallyremoved or installed without interfering with immediately adjacentmodules. In addition, the frame 210 may also physically support one ormore optical switch cores, which may also generally be referred to as“switch fabric,” of the switch subsystem 110.

[0039] As shown in this embodiment, the first platform 205 comprises (i)a plurality of I/O port modules 215 associated with the I/O subsystem130 of FIG. 1, (ii) a plurality of servo modules 225 and a managementcontrol subsystem (MCS) 235 associated with switch control subsystem 120of FIG. 1, and (iii) a first (primary) optical switch core 240associated with switch subsystem 110 of FIG. 1. Similarly, the secondplatform 206 comprises a plurality of additional I/O port modules 245, aplurality of (redundant) servo modules 250, a management controlsubsystem 255, and a second (redundant) optical switch core 260. Thethird platform 207 comprises a plurality of servo modules 265 thatcontrol various mirrors of the first and second optical switch cores 240and 260, which correspond to additional ports associated with I/O portmodules 245. Additionally, a light path test signal generator(s), alight path signal monitor(s), circuit breakers and/or alarm visualindication 270 may be located within the third platform 207. Forclarity, the elements forming the first platform 205 are described sincethese elements may be found in the second and/or third platforms 206 and207.

[0040] As shown in both FIGS. 2-4, the first optical switch core 240includes a first optical switch matrix 241 and a second optical switchmatrix 242. These matrices 241 and 242 are collectively positioned toroute light signals 250 between a port of a source I/O port module 215_(s) (“s” is a positive whole number) and a port of a destination I/Oport module 215 _(d) (“d” is a positive whole number), both moduleslocated in any of the platforms 205, 206 and 207 as shown in detail inFIG. 3. Although a two-bounce routing technique is shown, it iscontemplated that other light routing techniques may be used including athree-bounce routing technique in which a second bounce mirror 202optionally shown in FIG. 3 is positioned to assist in routing lightsignals from one optical switch matrix to another.

[0041] As shown in FIG. 4, one embodiment for each of the optical switchmatrices 241 and 242 includes multiple arrays 300 of micro-machinedmirrors. Each mirror (e.g., mirror 310) features a mirrored surface 311and torsional flexures 320 and 330 that enable the mirror 310 to adjustits physical orientation to reflect incoming light signals in anyselected direction. Herein, both the first and second optical switchmatrices 241 and 242 include Q micro-machined mirrors, where “Q” is lessthan or equal to the maximum number of I/O ports that can be supportedby the optical cross-connect switching system 100. For this embodiment,“Q” is greater than or equal to 64 but less than or equal to 1152(64≦Q≦1152). However, the present invention is not limited to anymaximum number of mirrors or I/O ports. It is contemplated, however,that the number of mirrors employed within the first and second opticalswitch matrices 241 and 242 may differ.

[0042] As generally shown in FIGS. 2, 5 and 6, the plurality of I/O portmodules 215 features two groups 216 and 217 of I/O port modules. Eachgroup, such as group 216 or 217 for instance, includes up to seventy-two(72) quad-port I/O port modules as shown in FIG. 5 that receive powerfrom one or more power supply modules denoted herein as “PSM”. Thecomponents forming an I/O port module is described below and shown inFIGS. 8 and 9. Thus, each I/O port module, such as I/O port module 215_(s) for example, features an external interface 400 for a plurality ofI/O ports 410 (e.g., four I/O ports). An I/O port 410 features a duplexsocket that is adapted to receive a duplex pair of optical fiber links,one optical fiber link routes a light signal to the I/O port 410 whilethe other routes light signals from the I/O port 410. This supportbi-directional optical connections. There is a small percentage (e.g.,less than 15%) of these I/O ports, however, that may be assigned as testaccess ports as described below.

[0043] Moreover, as shown in FIG. 6, upon receiving an incoming lightsignal over an optical fiber link 420, the I/O port module 215S performsa bridging operation by splitting the incoming light signal intomultiple (two or more) bridged light signals for routing to the firstand second optical switch cores 240 and 260. The bridged light signalsare routed through an internal optical interface 425 featuring opticalfiber ribbon links 430 and 440. For this embodiment, the “optical fiberribbon links” are ribbon cables having multiple optical fiber lines(e.g., two lines from each I/O port). The first optical switch core 240provides a primary optical path. The second optical switch core 260provides a redundant optical path in the event the first optical switchcore 240 is not operating properly. The optical switch cores 240 and 260route the bridged light signals to a selected port of a destination I/Oport module (e.g., I/O port module 215 _(d)) via optical fiber ribbonlinks 450 and 460.

[0044] Upon receiving light signals from both the first and secondoptical switch cores 240 and 260, the I/O port module 215 _(s) providessmall percentage optical tap signals of the received light paths to therespective servo modules, which in turn determine light signal quality.The respective servo modules will convey light signal quality for eachrespective light path to the I/O port module, using a digital protocolover an electrical communication link 505 to the I/O port module asshown in FIG. 7. The I/O port module 215 _(s) will in turn, determine(i.e. select) which light signal has the higher signal quality andoutputs that signal via interface 400. In most cases, the signal qualityof the two light paths presented to the I/O port module will be of thesame signal quality and may have a relatively low optical loss ofapproximately seven decibels (7 dB) or less.

[0045] Referring now to FIGS. 2 and 7, each servo module 225 isconfigured to receive optical tap signals from one or more I/O portmodules. Herein, servo module 225 _(i) is configured to receive opticaltap signals via link 500 from I/O port module 215 _(s). These opticaltap signals provide feedback to indicate a percentage of the bridgedlight signals and also allow for light to be injected under certainconditions. In response to receiving optical tap signals via link 500,the servo module 225 _(i) provides mirror control signals over link 510to the first optical switch core 240. The mirror control signals arerouted via a unique communication path to an optical switch (e.g., amicro-machined mirror) and are associated with the port of the I/O portmodule 215 _(s) through which the incoming light signal was routed. Themirror control signals are used for proper adjustment of the physicalorientation of the mirror.

[0046] The I/O port module 215 d provides optical tap signals over link530 to servo module 225 _(j). In response to receiving the optical tapsignals from I/O port module 215 _(d), the servo module 225 _(j)provides mirror control signals via link 540 to the first optical switchcore 240. The mirror control signals are routed via a uniquecommunication path to a micro-machined mirror associated with a selectedport of the I/O port module 215 _(d) from which the light signal wouldbe output. Herein, sensing the optical tap (feedback) signals, the servomodule 225 _(j) determines the light signal quality and conveys lightsignal quality information for each light path using a digital protocolover (electrical) link 535. Thereafter, the I/O port module 215 dchooses the selected port (i.e. port having the best light signalquality).

[0047] Collectively, the optical tap signals, mirror control signals andlight signal quality information, which are routed over links 500, 510,530, 540, 505 and 535, are used by servo modules 225 _(i) and 225 _(j)for adjustment of the physical orientation of mirrors to make aconnection between I/O port module 215 _(s) and 215 _(d).

[0048] Additionally, I/O port modules 215 _(s) and 215 _(d) alsotransfer optical tap signals via links 520 and 550, respectively.Similar to the above description, these optical tap signals establishthe redundant optical path by altering the physical orientation of oneor more micro-machined mirrors of the second optical switch core 260using mirror control signals over links 560 and 570 and light signalquality information via links 525 and 555.

[0049] In the event that no optical power is presented to the I/O portmodule 215 _(s), a substitute light signal may be injected from theservo module 225 _(i) via link 500. An alignment laser may be used asshown in FIG. 11 described below. This process of light substitutionallows for connection establishment and verification when no input lightis present to the I/O port module 215 _(s). The substitute light sourcecan be within the same wavelength range (e.g. 1100 nanometers “nm” −1700nm) as the allowed input light signal range. In one embodiment, thelight source or method of injection would be chosen to not interferewith attached equipment's select operational wavelength range. Choosinga different wavelength source on the servo module and/or a wavelengthspecific splitter and/or filter on the I/O port module could do thisparticular embodiment.

[0050] The management control subsystem 235 (see FIG. 2) enablescommunications between two or more servo modules placed within the sameor different platforms. The management control subsystem 235 includes atleast one servo control module 236 and an optional network controlmodule 238. In one embodiment, the servo control module (SCM) 236ensures communication between at least servo modules 225 _(i) and 225_(j) that control mirrors associated with the first optical switch core240. The network control module (NCM) 238 manages the execution ofconnection configurations for the whole cross-connect switching systemand ensures communications between multiple servo control modules 236and 237. The same architecture is used to control optical switcheswithin the second optical switch core 260 as shown.

[0051] II. General Architecture of the I/O Port Modules

[0052] Referring now to FIGS. 8 and 9, an exemplary embodiment of an I/Oport module (e.g., I/O port module 215 _(s)) and its communications overoptical switch cores 240 and 260 is shown. I/O port module 215 _(s)includes a data propagation circuit 600 for each I/O port and a controlcircuit 670. Thus, in the event that the I/O port module 215 _(s) isconfigured with four I/O ports, four data propagation circuits areimplemented on the I/O port module 215 _(s) as represented. Only thedata propagation circuit 600 for one of the I/O ports of I/O port module215 _(s) (e.g., i^(th) I/O port) is shown in detail for clarity sake.

[0053] In one embodiment, the data propagation circuit 600 comprises anoptical switch 610, a (passive) splitter 620 and a plurality of tapcouplers 630 ₁-630 ₄. The plurality of tap couplers 630 ₁-630 ₄correspond to the pairs of optical fibers found in optical fibber ribbonlinks 430 and 440. The control circuit 670 comprises a programmablememory 680, a processing unit 685 and status identification components690.

[0054] As shown, each port of the I/O port module 215 _(s) supportsfull-duplex communications. Thus, an incoming light signal 606 receivedover port 605 is routed to the splitter 620. The splitter 620effectively performs a bridging operation by splitting the incominglight signal 606 into bridged light signals 625, which collectively havethe same power level (energy) as the light signal 606. In oneembodiment, when the splitter 620 is a 50/50 splitter, the bridged lightsignals 625 have equal power levels. However, it is contemplated thatsplitter 620 may produce bridged light signals 625 havingdisproportionate power levels.

[0055] The bridged light signals 625 are routed through the tap couplers630 ₁ and 630 ₂. Attached to servo module 225 _(i) and servo module 225_(i+1) via optical tap links 500 and 520, the tap couplers 630 ₁ and 630₂ are used to monitor the power level of light signals 635 and 636propagating through optical fiber ribbon links 430 and 440 (referred toas “outgoing light signals”). This enables the servo modules 225 _(i)and 225 _(i+1) to verify the connectivity of the splitter 620 to opticalfiber ribbon links 430 and 440 and to detect unacceptable variances inoptical performance of the light signal. As shown for this embodiment,the tap couplers 630 ₁ and 630 ₂ may separate the bridged light signalsinto signals having disproportionate power levels in order to maximizethe power levels of the outgoing light signals propagating throughoptical fiber ribbon links 430 and 440. For example, where the tapcouplers 630 ₁ and 630 ₂ may operate as 90/10 splitters, the outgoinglight signals 635 and 636 have ninety (90%) of the total power level ofthe bridged light signal while the tap optical signals 640 and 641 haveonly ten percent (10%).

[0056] Referring to FIG. 8, tap couplers 630 ₃ and 630 ₄ are configuredto receive incoming light signal 650 and 655 via optical fiber ribbonlinks 430 and 440, respectively. The tap couplers 630 ₃ and 630 ₄effectively separate the light signals 650 and 655 into correspondingpairs of light signals having disproportionate power levels (e.g.,signals 661, 662 and 663, 664). Signals 662 and 664 having the lowerpower level are provided to the servo module 225 _(i) and servo module225 _(i+1) via links 500 and 520 for monitoring the power levels of thelight signals 661 and 663, without the light signals 661 and 663experiencing substantial signal degradation. The signals 662 and 664 maybe light signals that undergo O/E conversion at the I/O port module 215_(s) or at the servo modules 225 _(i) and 225 _(i+1) as shown in FIG.11. The tap couplers 630 ₃ and 630 ₄ are shown as 90/10 splitters;however, tap couplers 630 ₃ and 630 ₄ may be any selected ratio,including 50/50.

[0057] The light signals 661 and 663 are routed to the optical switch610 of a destined I/O port. The control circuit 650 on the I/O portmodule 215 _(s) determines which of the pair of light signals 661 and663 has the best signal quality based on conveyed light signal qualityinformation from the servo modules via links 505 and 525 as brieflydescribed below. Parameters used to determine light signal qualityinclude measured optical signal intensity/power, extinction ratio, andthe like. The light signal quality information to the I/O port modulemay be conveyed as failed due to the servo module service operations,high bit error rate, an external light path has failed, and the like.The light signal 661 or 663 with the best signal quality is outputthrough the I/O port 605. Of course, it is contemplated that the lightsignal output operations described for I/O port i are applicable to I/Oport j as shown.

[0058] It is contemplated that an I/O port of the I/O port module 215_(s) may be configured as a test access port. A “test access port” is anI/O port that is used for monitoring light signals routed throughanother port. Normally, the test access port receives a portion of thepower level of a light signal routed through a selected optical switch(e.g., micro-machined mirror). For example, as shown in FIG. 10, an I/Oport 218 of the I/O port module 215 _(s) is configured for coupling witha monitoring device 219 (e.g., a bit error rate “BER” monitor incombination with an optical-electrical “O/E” converter, etc.) to monitora power level of a light signal routed to the i^(th) I/O port from anoptical switch.

[0059] Referring back to FIG. 8, the control circuit 670 comprises theprogrammable memory 680 in communication with the processing unit 685(e.g., FPGA). The programmable memory 680 contains software and otherinformation used by the processing unit 685 to provide selection of thebest quality signal based on digital electrical signaling from servomodule 225 _(i) and servo module 225 _(i+1) over links 505 and 525,respectively. Also, programmable memory 680 includes information used bythe processing unit 685 to control the state of the statusidentification components 690 (e.g., light emitting diodes “LEDs”). Thestate of the status identification components 690 identifies (1) whethereach I/O port is operational and/or (2) whether the I/O port module isoperational. The processing unit 685 is further in communications withoptical switches of each data propagation circuit employed in the I/Oport module 215 _(s) in order to receive switch status signals andprovide switch control signals. As shown for clarity, processing unit685 provides optical switch 610 with switch control signals forreceiving switch status signals and selecting either light signal 661 orlight signal 663.

[0060] III. General Architecture of the Servo Modules

[0061] Referring now to FIG. 11, an exemplary embodiment of the servomodule (e.g., servo module 225 _(i)) is shown. In one embodiment, theservo module 225 _(i) comprises two separate modules in communicationover connectors 705 and 790. These separate modules are referred to asan “optical detector module” 700 and a “servo mirror control module”750.

[0062] The optical detector module 700 comprises a first processing unit710, memory 715, a plurality of detection/modulation (DM) circuits 716and status identification components 717. As shown, the optical detectormodule 700 features sixteen (16) DM circuits 716 to support four (4)quad-port I/O port modules. Each DM circuit 716 includes ananalog-to-digital (A/D) converter 720, a laser 725, optical-electrical(O/E) detectors 730 and 731, and optional amplifiers 735 and 736.

[0063] The servo mirror control module 750 comprises a second processingunit 755, a memory 760, a plurality of mirror signal detection andgeneration (SDG) circuits 761, a third processing unit 775 and statusidentification components 795. The SDG circuits 761 correspond in numberto the DM circuits 716 of the optical detector module 700. Each SDGcircuit 761 features an A/D converter 765, a digital-to-analog (D/A)converter 770, hinge position sensors 780-781 and high voltage (HV)mirror drivers 785-786.

[0064] As shown in FIG. 11, the optical detector module 700 is removablycoupled to the servo mirror control module 750. This allows the opticaldetector module 700 to be “hot swapped” from a backplane, which featuresconnectors 705 and 790 connecting the optical detector module 700 to theservo mirror control module 750, without disrupting the servo mirrorcontrol module's 750 ability to hold the mirrors in their existingpositions for an extended period of time. This “hot swapping” of theoptical detector module 700 allows for repair or upgrade of the opticaldetector module 700. Optical detector module 700 receives optical tap(feedback) signals 640 and 662 from one or more I/O port modules (e.g.,I/O port module 215 _(s) via link 500) and can transmit optical controlsignals 726 from the laser 725 for alignment of light signalstransferred between two I/O port modules. The optical tap signal 640 isbased on an input light signal that is routed to the switch fabric.

[0065] More specifically, with respect to servo module 225 _(i), the O/Edetectors 730 and 731 are coupled to tap couplers 630, and 6303 of FIGS.8-9. More specifically, the O/E detectors 730 and 731 are configured todetect incoming, optical tap signals 640 and 662, convert the opticaltap signals 640 and 662 into corresponding electrical control signalsmeasuring a power level of the outgoing light signal, and optionallyroute the electrical control signals to corresponding amplifiers 735 and736. The (amplified) electrical control signals are provided to the A/Dconverter 720. The A/D converter 720 converts the electrical controlsignals into measured power sense signals 644 of a digital form. Themeasured power sense signals 644 are provided to the first processingunit 710.

[0066] Herein, the first processing unit 710 may perform a number ofoperations based on the electrical control signals such as thresholdcrossing, LOS integration, input/output power ratio analysis and thelike. Software and other information necessary for performing theseoperations may be obtained from the memory 715 by the first processingunit 710. Herein, memory 715 can be non-volatile memory such asnon-volatile random access memory, electrically erasable programmableread only memory (EEPROM) and the like.

[0067] The optical detector module 700 includes multiple statusidentification components 717 (e.g., light emitting diodes “LEDs”). Afirst LED 718 identifies whether any operational faults associated withthe servo module 225 _(i) have occurred. A second LED 719 indicates whenthe optical detector module 700 is in service.

[0068] Referring still to FIG. 11, in this embodiment, the servo mirrorcontrol module 750 comprises the second processing unit 755 that iscoupled to both the first processing unit 710 and the third processingunit 775. For instance, in order to adjust the switch fabric in responseto the measured power sense signals 644, the second processing unit 755receives information representative of the measured power sense signalsfrom the first processing unit 710 via connectors 705 and 790. Thesecond processing unit 755 further receives information representativeof measured power sense signals for the light signal at a targeted I/Oport. This information is provided by the SCM 236 over link 580 via thethird processing unit 775. This assists in reducing errors in adjustingthe torsional flexures of the mirrors.

[0069] Upon receipt of these measured power readings, the secondprocessing unit 755 controls a particular SDG circuit corresponding to amirror associated with the I/O port over which the tapped light signalwas routed. The control involves slight mirror orientation adjustmentsif the power level readings differ substantially.

[0070] In particular, a first hinge position sensor 780 senses aposition of a mirror via link 510 from the first optical switch core240. The sensed position signal is routed to the A/D converter 765,which is subsequently placed in a digital format before routing to thesecond processing unit 755. When the servo module 2251 is adjusting theswitch fabric, the second processing unit 755 transfers mirror controlsignals to the D/A converter 770. The mirror control signals are routedto HV driver 785 and applied to a selected mirror of the first opticalswitch core in order to adjust the amount of torsional flexure along afirst dimensional plane (e.g., X-axis). This is accomplished to minimizethe loss experienced by the light signal.

[0071] A second hinge position sensor 781 senses a position of a mirrorfor the first optical switch core along a second dimensional plane(e.g., Y-axis). The sensed position signal is routed to the A/Dconverter 765, which is subsequently placed in a digital format beforerouting to the second processing unit 755. When the servo module 225_(i) is adjusting the switch fabric, the second processing unit 755transfers mirror control signals to the D/A converter 770. The mirrorcontrol signals are routed to HV driver 786 and are applied to theselected mirror of the first optical switch core in order to adjust theamount of torsional flexure along the second dimensional plane. Thespecifics of the hinge position sensors 780 and 781 are described in aPCT application entitled “Micromachined Members Coupled for RelativeRotation By Torsional Flexure Hinges” (International Publication No. WO00/13210) published on or around Mar. 9, 2000.

[0072] In another embodiment, when I/O port module 215 _(s) is thedestination of a light signal, the second processing unit 755 receivesinformation representative of the measured power sense signalsassociated with the optical tap signal 662 that has been analyzed by thefirst processing unit 710. The optical tap signal 662 is based on anoutput light signal being routed from an I/O port. In this situation,the third processing unit 775 receives information associated with themeasured power sense signals from a source I/O port as reported by SCM236 over link 580.

[0073] IV. Redundant Architecture of the Optical Cross-Connect SwitchingSystem

[0074] Referring now to FIG. 12, a block diagram of an alternativeembodiment of the architecture of the optical cross-connect switchingsystem of FIG. 1 is shown which includes redundant protectioncapabilities. Redundancy is desired in order to increase the reliabilityof such an optical cross-connect switching system. Aside from the I/Oport modules, all other modules are duplicated to obtain the desiredredundancy. Thus, it is necessary for light signals from a source I/Oport module 215 _(s) to be routed to a destination I/O port module 215_(d) through two optical paths, namely a primary optical path 800 usinga first optical switch core 240 and a redundant optical path 810 using asecond optical switch core 260.

[0075] With respect to the primary optical path 800, a servo module 225_(i) is connected to both the source I/O port module 215 _(s) and thefirst optical switch matrix (not shown) of the first optical switch core240. In particular, the servo module 225 _(i) controls the physicalorientation of a mirror of the first optical switch matrix thatcorresponds to the source I/O port module 215 _(s). To establish andmaintain the primary optical path 800 for the light signal, the servomodule 225 _(i) needs to communicate with other servo modules such asservo module 225 _(j). Thus, a servo control module (SCM) is implementedto support such communications, possibly through a time-slot switchingarrangement.

[0076] As shown, the SCMs 236 ₁-236 ₂ are also duplicated so that eachservo module 225 is connected to at least two SCMs 236 ₁-236 ₂. Thus, inthe event that the SCM 236 ₁ fails, the primary optical path 800 remainsintact because communications between the servo modules 225 _(i) and 225_(j) are maintained via redundant SCM 237 ₁. The transfer isaccomplished by temporarily halting the adjustment of (i.e. freezing)the mirrors inside the first optical switch core 240 while control istransferred from SCM 236 _(i) to SCM 237 ₁. The SCMs 236 ₁ and 237 ₁associated with the first optical switch core 240 are in communicationvia a network control modules (NCMs) 238 ₁ and 238 ₂ for example.

[0077] With respect to the redundant optical path 810, a servo module225 _(i+1) is connected to both the source I/O port module 215 _(s) andone or more mirror(s) of a first optical switch matrix (not shown) ofthe second optical switch core 260. Another servo module 225 _(j+1) isconnected to both the destination I/O port module 215 _(d) and one ormore mirror(s) of a second optical switch matrix (not shown) of thesecond optical switch core 260. The orientation of these mirrorsproduces the redundant optical path 810.

[0078] To establish and maintain the redundant optical path 810 for thelight signal, a SCM 2362 may be implemented with a dedicated time-slotswitching arrangement in order to support continuous communicationsbetween the servo module and another redundant servo module associatedwith the destination I/O port module. As shown, the SCM 236 ₂ is alsoduplicated so that each servo module 225 _(i+1) and 225 _(j+1) isconnected to at least two SCMs 236 ₂ and 237 ₂. Thus, the redundantoptical path 810 is maintained even when one of the SCMs 236 ₂ and 237 ₂fails. The SCMs 236 ₂ and 237 ₂ associated with the second opticalswitch core 260 communicate via the first NCM 238 ₁ and the second NCM238 ₂, respectively. The second NCM 238 ₂ is in communication with thefirst NCM 238 ₁ to allow all SCMs and servo modules to communicate forcoordination of the primary optical path 800 and the redundant opticalpath 810.

[0079] V. Signaling Interface

[0080] The present invention includes alternate embodiments forrealizing a signaling interface between optical cross-connect switchesand attached network equipment (ANE). Referring to FIG. 13, opticalcross-connect switches (OXCs) 1300 are deployed in a telecommunicationsnetwork. An optical cross-connect switch can also be referred to hereinas optical cross-connect switching system, OXC, or opticalcross-connect. Attached to the optical cross-connect switches in atelecommunications network is one or more pieces of attached networkequipment (ANE) 1302. The attached network equipment (ANE) 1302 includestelecommunication network devices such as a wavelength divisionmultiplexed (WDM) line terminals, SONET add/drop multiplexers, internetprotocol (IP) routers, additional optical cross-connect switches andAsynchronous Transfer Mode (ATM) switches which are also collectivelyreferred to as client equipment. WDM line terminals provideinterconnection between sites and are also terminating devices includedin SONET add/drop multiplexers, internet protocol (IP) routers, orAsynchronous Transfer Mode (ATM) switches. The present inventionestablishes a signaling interface between the optical cross-connects1300 and attached network equipment (ANE) 1302.

[0081] There are a number of reasons for establishing a signalinginterface between the optical cross-connects 1300 and attached networkequipment (ANE). One reason is to allow the other network equipment inthe telecommunications network to provision connections through the OXC.It is very desirable to allow other equipment to set up a connectionthrough the OXC in an automated manner, rather than manuallyprovisioning such connections. Another reason is to provide real-timeperformance monitoring and other management information to the opticalcross-connects 1300 from the attached network equipment 1302. Byproviding a signaling interface where performance information isprovided back to the optical cross-connects 1300, expensive monitoringelements are not needed inside the optical cross-connects 1300 and costsare saved. The attached network equipment usually already haveelectronic components for monitoring signals, such asoptical-to-electrical-to-optical converters (OEOs or O/E/Os), in orderto extract such information from optical signals. Thus, the electronicsfor monitoring do not need to be duplicated inside the opticalcross-connects 1300 when they are already provided in the attachednetwork equipment 1302. Instead the optical cross-connects 1300 canobtain the real-time performance monitoring and other managementinformation from the other network equipment that is attached to theoptical cross-connects 1300 through a signaling channel. Another reasonto establish a signaling interface is so that the attached networkequipment 1302 can obtain monitoring and other management informationreal-time from the optical cross-connects 1300. The opticalcross-connects 1300 can similarly monitor received optical signals onits input ports and provide information back to the attached networkequipment 1302. Preferably, the optical cross-connects 1300 only monitorthe optical power of the received optical signals by tapping off a smallpercentage of the energy of the optical signal and useoptical-to-electrical converters (OEs or O/Es) to determine the opticalpower without using O/E/Os.

[0082]FIG. 13 illustrates a block diagram of an out-of-band signalinginterface between an optical cross-connect switch 1300 and attachednetwork equipment 1302. The signaling interface is realized by using anout-of-band communication channel over a network 1304 which may also bereferred to as an out-of-band signaling channel. In-band communicationchannels are those used by the optical cross-connect switch 1300 toswitch data signals on the one or more data signals lines 1306A-1306N.An out-of-band communication channel is a communication channel otherthan that used by the optical cross-connect switch 1300 to switch itsdata signals on the data lines 1306A-1306N. The in-band communicationchannels used to switch data signals on the data lines 1306A-1306N bythe optical cross-connect switch 1300 are light signals, also referredto as photonic signals or optical signals, that are carried in opticalfibers. The data lines 1306A-1306N are not used for the signalinginterface because these lines carry high-bandwidth signals. To convertoptical signals in the optical domain into electrical signals in theelectrical domain to extract signaling information is a very expensiveprocess. Indeed, a major reason for using an all-optical cross-connectis to avoid converting signals from the optical domain to the electricaldomain. The out-of-band signaling channel is provided on a network 1304such as a LAN, a MAN, the internet or other WAN. Each of the data lines1360A-1306N is bi-directional to provide duplex data communicationchannels. The data lines 1306A-1306N in one embodiment include at leasttwo optical fibers for data flow in each direction between the opticalcross-connect switch and the attached network equipment 1402 to providefull duplex data communication channels. In another embodiment, each ofthe data lines 1306A-1306N is a single optical fiber to providebi-directional signal flow in both directions and can be full or halfduplex data communication over a single optical fiber. Full duplex isaccomplished over a single optical fiber by transmitting and detectingsignals in the single optical fiber at each end. [NOTE—IS THIS CORRECTTO SAY FOR FULL DUPLEX OVER A SINGLE FIBER. WE HAVE BEEN TRYING TO MOVETOWARDS SAYING “TRANSPORT” SO WHEN AN OPTICAL RECEIVE AND TRANSMITTERARE NOT PROVIDED. PLEASE COMMENT. WEA] The network 1304 also provides abi-directional out-of-band signaling channel so that signals can bereceived and transmitted in each direction between the opticalcross-connect switch and the attached network equipment 1402 and othernetwork equipment coupled to the network 1304. [IN THIS CASE IT SHOULDBE OK TO SAY TRANSMIT AND RECEIVE BECAUSE IT'S THE SINGALING INTERFACE.CORRECT?] The out-of-band signaling channel can be either full duplex orhalf duplex in providing bi-directional data communication.

[0083] Data signals from the optical cross-connect switch 1300 on thedata lines 1306A-1306N are coupled into the attached network equipment1302. The data lines 1306A-1306N are a light transmission media, such asoptical fibers, coupled between the optical cross-connect switch 1300and the attached network equipment 1302 to carry or transport the lightpulses or photon pulses of the data signals there-between. That is, theattached network equipment 1302 is coupled or attached to the opticalcross-connect switch 1300 to accept data signals transported over theone or more data lines 1306A-1306N. Data signals from the attachednetwork equipment (ANE) 1302 on the data lines 1306A-1306N are coupledinto the optical cross-connect switch 1300. The optical cross-connectswitch 1300 is coupled or attached to the attached network equipment1302 to accept data signals transported over the one or more data lines1306A-1306N.

[0084] The optical cross-connect switch 1300 includes the networkmanagement controller (NMC) 1310 (also previously referred to herein asa network control module (NCM)), one or more I/O port cards 1314A-1314Nand 1315A-1315N, and the optical switch fabric 1312. The optical switchfabric generates optical paths therein in order to cross-connect (alsoreferred to as route or switch) optical signals from an I/O port card onthe input side to an I/O port card on the output side. The optical pathsare bi-directional in that the optical signal can flow in eitherdirection with the optical path coupled to either an input port or anoutput port of a port card. I/O port cards can also be referred to asline cards, port cards, or I/O port modules as previously used herein.Each of the one or more I/O port cards 1314A-1314N and 1315A-1315N ofthe optical cross-connect switch 1300 includes an optical input port andan optical output port to couple to the optical fibers of the fullduplex data lines 1306A-1306N. Port cards 1314 can also include somesimple monitoring functions by tapping off a small percentage of theenergy of the optical signal and converting it into an electrical signalusing an inexpensive O/E. However, port cards 1314 do not need afull-fledged receiver for extensive monitoring of parameters such as abit error rate or the presence of a particular frame because thesignaling interface of the present invention is provided in order toacquire such information from other network equipment.

[0085] The attached network equipment 1302 includes a network managementcontroller 1320 and one or more I/O port cards 1321A-1321N (alsoreferred to as line cards or herein previously as I/O port modules).Each of the one or more I/O port cards 1321A-1321N includes anoptical—electrical-optical converter 1322A-1322N on its data input portsto couple to optical fibers of the data lines 1306A-1306N. The one ormore optical—electrical-optical converters 1322A-1322N first convert theoptical signals on the data lines 1306A-1306N into electrical signalsand then convert the electrical signals into optical signals.

[0086] The one or more optical—electrical-optical converters 1322A-1322Ncan be used for a number of reasons including to generate electricalsignals to monitor the optical signal as well as to amplify (i.e.regenerate) low level incoming optical signals. In the conversionprocess, the one or more optical—electrical-optical converters1322A-1322N provide information regarding the optical signals inelectrical form which is tapped for monitoring purposes as theelectrical signals 1323A-1323N. The electrical signals 1323A-1323N mayinclude information from other sources of the respective port card1315A-1315N that may be of relevance to the optical cross-connectswitch. The one or more optical—electrical-optical converters1322A-1322N and their electrical signals were originally used in theattached network equipment 1302 to facilitate its functionality andmonitor its performance and not provide feedback to an opticalcross-connect switch.

[0087] The electrical signals 1323A-1323N are coupled into the networkmanagement controller (NMC) 1320 of the attached network equipment 1302.In one embodiment, the electrical signals 1323A-1323N, or arepresentation thereof, are signaled back to the optical cross-connectswitch 1300 over the out-of-band signaling channel on the network 1304.The electrical signals 1323A-1323N, or a representation thereof, aretransmitted from the network management controller 1320 in the attachednetwork equipment 1302 to the network management controller 1310 in theoptical cross-connect switch 1300. In this manner, the attached networkequipment 1302 signals to the optical cross-connect switch 1300. In asimilar manner with differing information, the optical cross-connectswitch 1300 can signal to the attached network equipment 1302 over theout-of-band signaling channel.

[0088] The optical—electrical-optical converters 1322A-1322N areexpensive and as a result of being already available in the attachednetwork equipment 1302, they are not needed in the optical cross-connectswitch 1300 if the signaling interface of the present invention isprovided. This can provide considerable cost savings when purchasingoptical cross-connect switches 1300.

[0089] In FIG. 13, the attached network equipment 1302 that is coupledto the optical cross-connect switch 1300 is a WDM line terminal 1302which also includes a wave division multiplexer/demultiplexer 1324 alongwith the network management controller 1320 and the one or more portcards 1321A-1321N with the optical—electrical-optical converters1322A-1322N. The wave division multiplexer/demultiplexer 1324 couples toa pair of optical fibers on one end to carry wave divisioned multiplexedsignals 1326 in each direction for full duplex communication and one ormore pairs of optical fibers on an opposite end to couple to the I/Oport cards 1321A-1321N. The wave division multiplexer/demultiplexer 1324multiplexes multiple light signals received from respective opticalfibers in one direction into a wave division multiplexed signal 1326having multiple light signals of different wavelengths carried over oneoptical fiber, The wave division multiplexer/demultiplexer 1324demultiplexes a wave division multiplexed signal 1326 in an oppositedirection having multiple light signals of different wavelengths carriedover one optical fiber into multiple light signals for transmission tothe optical cross-connect switch 1300 over the data lines 1306A-1306N.The wave division multiplexed signal 1326 provides greater databandwidth and channel capacity over an optical fiber.

[0090] The network connection to the network 1304 for the out-of-bandsignaling channel is an Ethernet, an RS232 or other similar connectionconnecting together the network management controllers (NMCs) (alsopreviously referred to as a network control module (NCM)) of the opticalcross-connect switch 1300 and the attached network equipment 1302.Because the out-of-band signaling channel is provided over the network1304, other network equipment or monitoring stations can receiveinformation and transmit information or control signals over the out-ofband signaling channel regarding the network, the network equipment andthe optical network components connected to the network. Thus,management of the network can be facilitated regarding the opticalcross-connect 1300, the attached network equipment 1302, and othernetwork equipment using the out-of-band signaling channel. Theout-of-band signaling channel over the network can be considered acentralized signaling interface.

[0091] Referring now to FIG. 14 a block diagram of a decentralizedsignaling interface between an optical cross-connect switch 1400 andattached network equipment 1402 is illustrated. The decentralizedsignaling interface is provided by one or more dedicated signal lines1404A-1404N between the optical cross-connect switch 1400 and theattached network equipment 1402. The one or more dedicated signal lines1404A-1404N can be formed by using low-cost multimode (MM) opticalfibers or by using low cost electrical wire links.

[0092] The one or more dedicated signal lines 1404A-1404N replaces theout-of-band signaling channel of the network 1304. Whereas theout-of-band signaling channel of the network 1304 provided signalsregarding switching each of the optical signals on multiplecommunication channels, one dedicated signal line 1404 providesinformation regarding switching of optical signals on one communicationchannel. Furthermore, the centralized signaling between the between theoptical cross-connect switch 1400 and the attached network equipment1402 was performed by the centralized NMCs 1310 and 1320 at a centralcontrol level. In contrast, decentralized signaling is performed by theI/O port cards (also referred to as line cards or herein previously asI/O port modules) at a line-card level which is a much lower level thanthe centralized NMC level.

[0093] In the embodiment illustrated in FIG. 14, the opticalcross-connect switch 1400 includes the network management controller(NMC) 1310, one or more I/O port cards 1414A-1414N (also referred to asline cards, port cards and I/O port modules), and the optical switchfabric 1312. Each of the one or more I/O port cards 1414A-1414N and1415A-1415N of the optical cross-connect switch 1400 includes an opticalinput port and an optical output port. Each of the one or more portcards 1414A-1414N further may include optical-electrical converters(O/E) 1416A-1416N if the dedicated signal line is an optical fiber. Theoptical-electrical converters 1416A-1416N of the optical cross-connectswitch are much less expensive than optical-electrical-opticalconverters (O/E/O) that might otherwise be needed therein.Optical-electrical converters (O/E) are typically a fiber optic receivermodule which includes a photodetector.

[0094] The attached network equipment 1402 includes one or more portcards 1421A-1421N (also referred to as line cards). Each of the one ormore port cards 1321A-1321N includes an optical—electrical-opticalconverter 1322A-1322N on its data input ports to couple to opticalfibers of the data lines 1306A-1306N. In the case the dedicated signallines 1404A-1404N are optical fibers, each of the one or more port cards1321A-1321N further includes an electrical-optical converter (E/O)1422A-1422N to convert electrical signals 1423A-1423N into opticalsignals. Electrical-optical converters (E/O) are typically a fiber optictransmitter module which include a semiconductor laser with controlelectronics. Optical-electrical-optical converters (O/E/O) are typicallya combination of an O/E converter coupled together with an E/Oconverter.

[0095] The attached network equipment 1402 that is illustrated coupledto the optical cross-connect switch 1400 is a WDM line terminal 1402. AWDM line terminal 1402 also includes a wave division multiplexer 1324along with the one or more port cards 1421A-1421N with theoptical-electrical-optical converters 1322A-1322N.

[0096] The one or more optical-electrical-optical converters 1322A-1322Nfirst convert the optical signals on the data lines 1306A-1306N intoelectrical signals and then convert the electrical signals into opticalsignals. The one or more optical—electrical-optical converters1322A-1322N are tapped to provide information regarding the opticalsignals in electrical form on the electrical signals 1323A-1323N. Theport cards 1421A-1421N of the attached network equipment 1402 detectother relevant information and communicate it directly to the respectiveport cards 1414A-1414N of the optical cross-connect switch 1400 over thededicated signal lines 1404A-1404N rather than signaling between thecentral NMCs 1310 and 1320. Similarly, port cards 1414A-1414N of theoptical cross-connect switch 1400 can detect relevant information andcommunicate it directly to the respective port cards 1421A-1421N of theattached network equipment 1402 over the dedicated signal lines1404A-1404N.

[0097] Having established a signaling interface, it can be used forseveral purposes. The signaling interface can be used to enable fastnetwork restoration through the optical cross-connect switch (OXC) inthe event of network failures. Network failures include signal failuressuch as a loss of signal (LOS) or signal degradation such as through abit error rate (BER) or other commonly know optical failure mechanisms.Attached network equipment (ANE) can detect failures in real time byusing its O/E/Os and convey this information to the opticalcross-connect switch over the signaling interface so that it can performnetwork restoration. The optical cross-connect switch is typicallywithout O/E/Os and may not be able to detect the failure due to theotherwise relatively simple monitoring usually found within an opticalcross-connect switch.

[0098] Another use for the signaling interface is to allow attachednetwork equipment (ANE) to control the optical cross-connect switch(OXC). For example, the attached network equipment (ANE) could signal tothe OXC over the signaling interface in order for it to provide aparticular switch configuration.

[0099] Another use for the signaling interface is so that the opticalcross-connect switch can signal to the attached network equipment to setspecific parameters therein. For example during setting up a connection,the optical cross-connect switch may ask the attached equipment toadjust its transmitter power level.

[0100] Another use for the signaling interface is to allow attachednetwork equipment (ANE) to request a connection through the opticalcross-connect switch (OXC). The optical cross-connect switch (OXC) setsup the connection and informs the attached network equipment (ANE) whenits available.

[0101] Another use for the signaling interface is to perform protectionswitching between the OXC and the attached network equipment. Forexample, the signaling interface could be provided by one spare fiberfacility for N working facilities between the attached equipment and theOXC. If one of these N facilities fails, the signaling channel is usedby both devices to switch connections from the failed facility to thespare facility.

[0102] VI. Optical to Electrical to Optical Conversion

[0103] Specific configurations for building optical cross-connectswitching systems are disclosed herein. Optical-to-electrical-to-opticalconverters (O/E/Os) are included on input and output ports to an opticalswitch fabric, a core element of an optical cross-connect. Methods forperforming bridging, test access, and supporting redundant cores arealso disclosed.

[0104] Referring now to FIG. 15, a block diagram of an opticalcross-connect switch (OXC) 1500 is illustrated. An optical cross-connectswitch is also referred to herein as an optical cross-connect, an OXC,and an optical cross-connect switching system. The optical cross-connectswitch (OXC) 1500 includes an optical switch fabric 1510 (also referredto as the optical switch core) and various I/O port cards. The opticalcross-connect switch 1500 has one or more optical input ports1501A-1501N and one or more optical output ports 1502A-1502N provided byvarious I/O port cards which are also referred to herein as I/O portmodules or simply port cards. The various I/O port cards can include oneor more smart port cards 1504A-1504L and 1504A′-1504M′ (generallyreferred to as smart port cards 1504) and/or one or more passive portcards 1503A-1503N (generally referred to as passive port cards 1503).The optical switch fabric 1510 in one embodiment is an N×N opticalswitch core having N inputs and N outputs. The optical switch fabricgenerates optical paths therein in order to cross-connect (also referredto as route or switch) optical signals from an input side to an outputside. The optical paths are bi-directional in that the optical signalcan flow in either direction with the optical path coupled to either aninput port or an output port of a port card. Each input and output portand each input and output of the optical switch core is respectivelyassociated with an input and output path of one of the one or more portcards 1504 and 1503. The input path and the output path are paths overwhich the optical signals propagate in the port card relative to theoptical switch fabric 1510.

[0105] The port cards 1504 and 1503 can be classified as either passiveport cards or as smart port cards. The one or more smart port cardsinclude optical-electrical-optical converters (O/E/O) 1507 in an opticalinput path, an optical output path, or both their optical input andoutput paths. Optical-electrical-optical converters are also referred toherein as optical-to-electrical-to optical converters. The O/E/Os 1507are provided in an optical cross-connect switch for several reasons. TheO/E/Os provide a standardized interface with other equipment; enable anoptical cross-connect switch to perform detailed real-time performancemonitoring, such as bit error rates, and to determine failures in thenetwork using this monitoring; can isolate one segment of the networkfrom another segment; and can provide wavelength conversion. The one ormore passive port cards 1503 do not have an optical-electrical-opticalconverter (O/E/O) 1507 to provide optical-electrical-optical conversionin either of their optical input paths 1513 or optical output paths1514.

[0106] The smart port cards 1504A-1504M have an O/E/O 1507 in theiroptical input paths 1511 and not their optical output paths 1512. TheO/E/O 1507 in the optical input paths 1511 is also referred to being onthe input side of the optical cross-connect switch 1500. Locating anO/E/O on the input isolates the optical losses associated with anoptical cross-connect switch from the input optical signal.Additionally, an O/E/O on the input side can regenerate an input opticalsignal and provide a stronger optical signal for propagation through aswitch fabric of an optical cross-connect switch. An O/E/O on the inputside of an optical cross-connect switch (OXC) can also providewavelength conversion and/or translation before the signal is routedthrough the switch fabric of the optical cross-connect switch. That is,the O/E (optical receiver) of the O/E/O can accept a full range ofphoton frequencies and convert it into an electrical signal while theE/O conversion may be provided by a multimode laser for example that canbe tuned to a desired photon wavelength (i.e. frequency) output toprovide wavelength conversion. Otherwise, the E/O conversion may beprovided by a single mode laser for example which has the desired photonwavelength output as opposed to be tunable. Additionally, the O/E/O onthe input side can generate an electrical signal representing theincoming optical signals for monitoring purposes. A processor canprocess the electrical form of the incoming optical signals in a binarycoded form to make control decisions as well as pass performanceinformation to other network equipment regarding the input opticalsignals input. For example, the electrical signal may indicate the lackof an optical signal or errors in an optical signal.

[0107] The smart port cards 1504A′-1504L′ have an O/E/O 1507 in theiroptical output paths 1512 and not their optical input paths 1511. TheO/E/O 1507 in the optical output paths 1512 is also referred to as beingon the output side of the optical cross-connect switch 1500. Locating anO/E/O on the output path isolates the optical cross-connect switch fromthe network to which it is attached. For example negative opticalconditions or negative timing parameters may exist on the crossconnected signal output from the switch fabric, such as low opticalpower, wrong wavelength, poor spectral quality, overpower, etc. TheO/E/O within the output path can isolate these conditions from theoptical network. Additionally, an O/E/O on the output side canregenerate an the optical signal output from the switch fabric andprovide a stronger optical signal at the output of an opticalcross-connect switch. An O/E/O on the output side of an opticalcross-connect switch (OXC) can also provide wavelength conversion and/ortranslation after the signal has been routed through the switch fabricof the optical cross-connect switch. The optical signals that are inputinto the optical cross-connect switch may have a wide range ofwavelengths and the O/E/O can convert them into one or more desiredwavelengths as the output optical signal. Additionally, the O/E/O on theoutput side can generate an electrical signal representing the outgoingoptical signals from the optical cross-connect switch. A processor canprocess the electrical form of the outgoing optical signals in a binarycoded form to make control decisions as well as pass performanceinformation to other network equipment regarding the output opticalsignals. For example, the electrical signal may indicate the lack of anoptical signal and a failure in the optical cross-connect switch orerrors in an optical signal.

[0108] In any case, the smart port cards 1504 converts the opticalsignal in the optical path into an electrical form, process theelectrical signal if desired, generate a desired optical signal from theelectrical signal, and retransmit the optical signal over the respectiveoptical input or output path in optical form.

[0109] An optical—electrical-optical converter 1507 first converts aninput optical signal into an electrical signal. The electrical signalcan be tapped out to provide information regarding the input opticalsignal input into the O/E/O 1507. the O/E/O 1507 then converts theelectrical signal into an output optical signal. The output opticalsignal from the O/E/O is similar to the input optical signal into theO/E/O in that the same data is being carried but the optical signalamplitude may be amplified, wavelength converted or otherwise improvedin some way over that of the input optical signal. The O/E/O 1507provides the conversion with little delay in the data carried by theoptical signal.

[0110] While an O/E/O 1507 may be in both the optical input path of asmart port card (input side of OXC) and the output path of a smart portcard (output side of OXC), it is required only in one of the opticalpaths of one port card for the more sophisticated applications of theoptical cross-connect switches. Smart port cards 1504 in FIG. 15 of theoptical cross-connect switch 1500 illustrate this principle. Forexample, an optical path 1515A in the optical switch fabric 1510 couplesthe optical input path 1511 of the smart port card 1504A with theoptical output path 1514 in the passive port card 1503A. The opticalsignal is regenerated by the O/E/O 1507 in the optical input path 1511of the smart port card 1504A. As another example, an optical path 1515Bin the optical switch fabric 1510 couples the optical input path 1511 ofthe smart port card 1504B to the optical output path 1512 of the smartport card 1504N. In this example, the optical signals are monitored bythe O/E/O 1507 in the optical output path 1512 of the smart port card1504N. As yet another example, an optical path 1515C in the opticalswitch fabric 1510 couples the optical input path 1513 of the passiveport card 1503A with the optical output path 1512 of the smart port card1504B. In this example, the optical signals are regenerated by the O/E/O1507 in the optical output path 1512 of the smart port card 1504B.Because the O/E/O 1507 is rather expensive, using only one O/E/O 1507 ina smart port card 1504 saves significant costs.

[0111] The type of port card to use, smart or passive, depends on theapplication of the optical cross-connect 1500 in the communicationnetwork. For a simple provisioning application where the opticalcross-connect switch 1500 is used to set up optical connections, passiveport cards 1503 need only be utilized. For a more sophisticatedapplication where full-featured performance, fault management andoptical protection are desired, smart port cards 1504 are needed. Notethat a mixture can be used where some of the port cards in the opticalcross-connect 1500 are passive port cards 1503 and others are smart portcards 1504 such as that illustrated in FIG. 15.

[0112] Referring now to FIG. 16, a block diagram of an opticalcross-connect switch 1600 having a one and two tiered port cardarrangement is illustrated. The optical cross-connect 1600 has one ormore optical input ports 1601A-1601Z and one or more optical outputports 1602A-1602Z provided by the various port cards. In the two tieredport card arrangement of the optical cross-connect 1600, one or moresmart port cards 1604A-1604M and 1604A′-1604N′ (generally referred to as1604) are coupled to one or more passive port cards 1603A-1603N(generally referred to as 1603) to access the optical switch fabric 1610(also referred to as an optical switch core). That is, the optical inputpaths of the smart port cards are coupled to the optical input paths ofthe passive port cards and the optical output paths of the passive portcards are coupled to the optical output paths of the smart port cards.Thus, input optical signals on the optical input paths of the smart portcards are coupled into the optical input paths of the passive portcards. Output optical signals on the optical output paths of the passiveport cards are coupled into the optical output paths of the smart portcards in the two tiered port card arrangement. Note that an opticalsignal may or may not need to be passed through a smart port card beforebeing passed through a passive port card. The passive port card 1603Zillustrates this case. Thus, passive port cards alone as a single tieredport card arrangement can be intermixed within the two tiered port cardarrangements.

[0113] In either the single or two tiered port card arrangement in theoptical cross-connect switch 1600, only the passive port cards1603A-1603Z are used to access the optical switch fabric 1610. Theoptical signals on the optical input path 1613 and the optical outputpath 1614 of the passive port card 1603Z need to couple to an opticaloutput path 1612 and an optical input path 1611 respectively each havingan O/E/O 1507 in order to regenerate the optical signals. Exemplaryswitching of optical signals is illustrated in FIG. 16 by the opticalpaths 1615A-1615E in the optical switch fabric 1610. Unidirectional andbi-directional connections can be made through the optical cross-connectswitch between I/O port cards. Bi-directional connections are moretypically the case. The optical paths 1615A, 1615B and 1615E illustrateexemplary optical paths (also referred to as light paths) through theoptical switch fabric 1610 for unidirectional connections between I/Oport cards. The optical paths 1615C and 1615D illustrate exemplaryoptical paths through the optical switch fabric 1610 for bi-directionalconnections between I/O port cards. The settings of the optical switchfabric 1610 change in order to rearrange the optical paths between theI/O port cards as desired.

[0114] The passive port cards 1603A-1603Z in the optical cross-connect1600 provide control of the optical signals into and out of the opticalswitch fabric 1610. The smart port cards 1602A-1602M having the O/E/Os1507 provide regeneration, performance monitoring, fault management andprotection switching functions. By splitting the functionality of theport cards in this manner into the two tiered arrangement, replacementof faulty port cards can be less costly. The two tiered arrangement ofI/O port cards also allows a system to be deployed with passive portcards initially with smart port cards being added later as needed. Alsothe smart port cards typically have different power and coolingrequirements than the passive port cards, and may be located in separateshelves to provide additional cooling.

[0115] In addition to basic switching functions provided by an opticalcross-connect, it is desirable to provide bridging, test access andsupport for redundant optical switch fabrics (also referred to asredundant optical switch cores).

[0116] Referring now to FIG. 17, a block diagram of an opticalcross-connect 1700 is illustrated. The optical cross-connect 1700 hasone or more optical input ports 1701A-1701N and one or more opticaloutput ports 1702A-1702N provided by the various port cards. The opticalcross-connect 1700 includes smart port cards 1704A-1704N and1704A′-1704M′ that provide bridging for the optical switch fabric 1710.Bridging means that at least two optical paths are provided between portcards carrying the same optical signals. The optical switch fabric 1710illustrates exemplary optical signal paths 1715A-1715D and redundantoptical signal paths 1715A′-1715D′. If one optical path fails in theoptical switch fabric 1710, the redundant optical path in the opticalswitch fabric 1710 continues to handle the data carried by the opticalsignals. For example, if the optical path 1715A fails in the opticalswitch fabric 1710, the optical path 1715A′ continues to carry theoptical signals. The redundant optical path 1715A′ can be thought asbridging a gap in the optical path 1715A when it fails.

[0117] An optical path or the generation of optical signals in anoptical path can fail terminating the optical signal completely orgenerating bit errors at a high rate over that of the other opticalsignal or optical path. By monitoring the optical signal inputs and/oroutputs from the optical network equipment such as the opticalcross-connect switch, a determination can be made whether to switch fromone optical signal in one optical path to another. The optical path andor optical signal in the optical path can fail for a variety of reasonsincluding one or more faulty components or a failure in control.

[0118] To generate a redundant optical path in the optical cross-connectswitch 1700, an input optical signal is input into an input port such asinput port 1701A. In one type of smart port card, illustrated by smartport cards 1704A-1704N (generally referred to as 1704), the inputoptical signal is coupled into an O/E/O 1707 in the input path 1711. TheO/E/O 1701 converts the optical signal into an electrical signal whichis then converted back into an optical signal. The electrical signal isused to monitor the input optical signals. The O/E/O 1707 is coupled toan optical splitter 1708 to split the incoming optical signal into atleast two optical signals on at least two split optical paths 1721A and1722A. The splitter 1708 can be used to split the incoming opticalsignal into more than two split optical paths to provide greaterredundancy and reliability if desired but is typically not needed. Theoptical splitter 1708 in one embodiment is a passive optical coupler.While the data signal or pulses of light of the split optical signalsare the same, the energy level of the incoming optical signal can besplit equally or unequally into the at least two optical signals on theat least two split optical paths 1721A and 1722A. The at least two splitoptical paths are coupled into the optical switch fabric 1710 andswitched to another port card respectively over the optical paths 1715Aand 1715A′ for example. The redundant optical signals in the opticalpaths 1715A and 1715A′ are coupled into a switch 1709 of the smart card1704B for example over the split paths 1723B and 1724B respectively. Theswitch 1709 is an optical switch. As its output, the switch 1709 selectsbetween the at least two optical signals in the at least two splitoptical paths 1715A and 1715A′. The selected output of the opticalswitch 1709 is coupled into the optical output path 1712 of the smartport card and the output port 1702B of the optical cross-connect switch1700. In the case that one of the two optical signals in the at leasttwo split optical paths fails or has errors, the optical switch 1709 canselect the alternate optical path as its output to overcome the pathfailure or the errors.

[0119] In another type of smart port card, illustrated by smart portcards 1704A′-1704M′ (generally referred to as 1704′), an input opticalsignal at the input port is first coupled into a splitter 1708′ in theoptical input path 1711. The incoming optical signal is first split bythe splitter 1708′ into at least two optical signals on at least twosplit optical paths 1721C and 1722C for example. The at least twooptical signals on the at least two split optical paths 1721C and 1722Care then coupled into the optical switch fabric 1710 for switching. Inthe optical switch fabric 1710, the split optical signals are routedover different optical paths such as optical paths 1715C and 1715C′. Thesplit optical signals on the different optical paths are coupled intothe same switch of a port card such as switch 1709′ of the smart portcard 1704M′ via the optical paths 1723M and 1724M for example. Theswitch 1709′ is an optical switch. As its output, the switch 1709′selects between the at least two optical signals in the at least twosplit optical paths 1715C and 1715C′ for example. The selected output ofthe optical switch 1709′ is coupled into the optical output path 1712 ofthe smart port card and the output port 1702M of the opticalcross-connect switch 1700. In the case that one of the two opticalsignals in the at least two split optical paths fails or has errors, theoptical switch 1709′ can select the alternate optical path as its outputto overcome the path failure or the errors. The output of the opticalswitch is coupled into the O/E/O 1707′ on the smart port card forregenerating the optical signals. With the O/E/O 1707′ in the outputpath, regeneration is performed post split. In this manner, the O/E/Osdo not need to be duplicated in the input path and output path for eachconnection of a communication channel over the optical cross-connectswitch 1700. The monitoring provided by the O/E/Os 1707 and 1707′ in thesmart port cards in the optical cross-connect switch 1700, assist in theselection between the at least two optical signal in the at least twosplit optical paths by the optical switches 1709 and 1709′ respectively.If the monitoring determines that there is no signal at the output ofthe optical switch 1709′ and its known that there should be a signalpresent, the optical switch 1709′ can select the alternate path. If themonitoring determines that there is an input optical signal into thesplitter 1708 and its known that it should be present at the output of aswitch 1709, the alternate path can be selected.

[0120] In either case, the port cards of the optical cross-connectswitch 1700 of FIG. 17 split the incoming optical signal at an inputport into at least two split optical signals to propagate over twodifferent optical paths and provide redundancy in how the data signal isrouted over the optical switch fabric. The port cards then select whichof the at least two split optical signals to couple into an output portof the optical cross-connect.

[0121] Referring now to FIG. 18, a block diagram of an opticalcross-connect switch 1800 is illustrated. The optical cross-connectswitch 1800 is an alternate embodiment to provide bridging over anoptical switch fabric 1810. The optical cross-connect switch 1800 hasone or more optical input ports 1801A-1801N and one or more opticaloutput ports 1802A-1802N provided by the various port cards.

[0122] Using one type of smart port card, the incoming optical signal isfirst converted from an optical signal in the optical domain into anelectrical signal in the electrical domain and fanned out (i.e.electrically split into two equal electrical signals) by coupling intoto two optical transmitters (i.e. an electrical to optical convertersuch as a semiconductor laser). The two optical transmitters convert inparallel the electrical signal into two optical signals in the opticaldomain. The two optical signals generated by the two opticaltransmitters (electrical-optical converters) are substantially similar.The two optical signals are then routed through the optical switchfabric through differing optical paths. A selection is then made at theoutput of the optical switch fabric between the two optical signals inorder to generate the output optical signal from the opticalcross-connect. If one path of the two optical signals should fail, theopposite path is selected.

[0123] Using another type of smart port card, the incoming opticalsignal is optically split into two split optical signals which arerouted over the optical switch fabric. At the output of the opticalswitch fabric, the two split optical signals in the optical domain arecoupled into two optical receivers (each an optical to electricalconverter (O/E) such as a photodiode) to convert them into twoelectrical signals respectively in the electrical domain. The twoelectrical signals are then coupled into multiplexer to electronicallyselect which one of the two should be transmitted out the output port ofthe optical cross-connect by an optical transmitter (i.e. an electricalto optical converter such as a semiconductor laser). The opticaltransmitter converts the selected electrical signal in the electricaldomain into an optical signal in the optical domain.

[0124] Referring to FIG. 18, the optical cross-connect switch 1800 caninclude one or more smart port cards 1804A-1804N and/or one or moresmart port cards 1804A′-1804M′. In either case, the smart port cardsprovide two different optical paths through the optical switch fabric1801 for the same communication channel connection. For example, opticalpaths 1815A-1815D are one path for the communication channels whileoptical paths 1815A′-1815D′ are another both carrying the same datasignals. If one optical path should fail generating a gap in theconnection, the other path is selected to bridge the gap and to allow acontinuous flow of data for the given communication channel connection.Bridging in this manner increases the reliability of the opticalcross-connect.

[0125] The smart port cards 1804A-1804N include an optical receiver 1817(i.e. an optical to electrical converter (O/E) such as a photodiode)which is coupled to a pair of optical transmitters 1818A and 1818B (i.e.an electrical to optical converter (E/O) such as a semiconductor laser)in the input path 1811. Thus, in the input path 1811 of the smart portcards 1804A-1804N an optical-electrical-optical conversion (O/E/O) isperformed. In the output path 1812, the smart port cards 1804A-1804Ninclude an optical switch 1809 to select between two optical signals.The optical transmitters 1818A and 1818B generate the two paralleloptical signals that are routed over two paths in the optical switchfabric such as optical paths 1815A and 1815A′. The optical switch 1809selects between the two parallel optical signals to generate one as theoutput of the optical cross-connect 1800 on an output port. If theselected path should fail, the optical cross-connect switches to theother optical signal carried over the other optical signal path.

[0126] The smart port cards 1804A′-1804M′ include an optical splitter1808 in the input path 1811 to split the incoming optical signal intotwo split optical signals. The two split optical signals are coupledinto the optical switch fabric 1810 to be routed over two separateoptical paths. For example, the smart port card 1804A′ would couple asplit incoming optical signal into the optical paths 1815C and 1815C′ ofthe optical switch fabric. In the output path 1812, the smart port cards1804A′-1804M′ include a pair of optical receivers 1828A and 1828B, amultiplexer 1829, and an optical transmitter 1827. The pair of opticalreceivers 1828A and 1828B (i.e. an optical to electrical converter (O/E)such as a photo-diode) receive the split optical signals routed over thetwo separate optical paths. A benefit of locating these receivers afterthe switch fabric(s) is that they can accept a full range of wavelengthsof photons due to dense wave-length division multiplexed (DWDM) opticalsignals. The wide range of wavelengths of optical signals over theoptical paths in the optical cross-connect can exist due to DWDM. Beingable to cross-connect any optical signal to the O/E/O over a range ofwavelengths is desirable to provide wavelength conversion/translation inthe optical cross-connect switch. Another benefit is that if somenegative optical conditions or negative timing parameters exist in thecross connected optical signal from the switch fabric, such as lowoptical power, wrong wavelength, poor spectral quality, overpower, etc.within the cross-connect switch, it can be isolated by the O/E/O beforebeing output to the network. The split optical signals are convertedinto two electrical signals by the optical receivers 1828A and 1828B andcoupled into the multiplexer 1829. The two electrical signals can alsobe monitored locally to determine which should be selected to generatethe optical output signal. It can also be forced to switch by means ofexternal communication control, if external monitoring methods areemployed. The multiplexer 1829 electronically selects one of the twoelectrical signals to be coupled into the optical transmitter 1827 (anelectrical to optical converter (E/O) such as a semiconductor laser). Ifthe two signals being selected from have the same data and protocol, asexpected, it is envisioned that the monitored switching between the twowithin the multiplexer could be hitless, i.e. produce no errors on theselected electrical signal. This behavior is very beneficial to bridgeand roll applications and those that have Forward-Error-Correction dataencoding schemes. This would also apply to SONET and SONET like datastreams as well as those employing a ‘wave wrapper’ protocol. Theoptical transmitter 1827 converts the selected electrical signal in theelectrical domain into an optical signal in the optical domain fortransmission out over the output port of the optical cross-connect 1800.Thus, in the output path 1812 of the smart port cards 1804A′-1804M′ anoptical-electrical-optical conversion (O/E/O) is performed.

[0127] Bridging in this manner provides that if a path or a component inthe path fails, the other path and components can handle the data flowover the communication channel in the optical cross-connect. Adisadvantage to the bridging provided by the optical cross-connects 1700and 1800 is that fewer communication channels can be supported becauseof the redundant optical paths formed in the optical switch fabrics 1710and 1810 respectively. One way to alleviate this problem is to use aredundant optical switch fabric to provide the redundant path.

[0128] Referring now to FIGS. 19A-19G, block diagrams of embodiments ofoptical cross-connect switches 1900A-1900G are illustrated. The opticalcross-connect switches 1900A-1900G include port cards that providebridging by using two or dual optical switch fabrics (also referred toas optical switch cores). The incoming signal is split into at least twosignals with one portion being coupled into one optical switch fabricwith another portion of the signal being coupled into the other opticalswitch fabric. While one acts as an active optical switch fabric, theother acts as a redundant optical switch fabric, for each path throughthe system. Providing a redundant optical switch fabric also providesreliability in case there is a problem in control of one of the opticalswitch fabrics, Furthermore, the redundant optical switch fabricprovides hot swapability in that while one is having its optical switchfabric or other control systems updated or replaced, the other cancontinue to provide optical switching. The optical cross-connectswitches 1900A-1900G also includes a test access/monitor port card totest and monitor the optical paths through the two optical switchfabrics to determine if there is a failure mechanism or not.

[0129] Referring to FIG. 19A, the optical cross-connect 1900A includes afirst optical switch fabric 1910A and a second optical switch fabric1910B and has one or more optical input ports 1901A-1901N and one ormore optical output ports 1902A-1902N provided by the various portcards. The optical cross-connect 1900 also includes one or more smartport cards 1904A-1904N (generally referred to as 1904) and/or one ormore smart port cards 1904A′-1904M′ (generally referred to as 1904′).The optical cross-connect 1900 can also include one or more testport/monitor cards 1905. The smart port cards 1904A-1904N provide anO/E/O 1907 in their input paths while the smart port cards 1904A′-1904M′provide an O/E/O 1907′ in their output paths. The smart port cards1904A-1904N and 1904A′-1904M′ each have an optical splitter 1908 and1908′ respectively in their input paths. The smart port cards1904A-1904N and 1904A′-1904M′ each have an optical switch 1909 and 1909′respectively in their output paths. The O/E/Os 1907 and 1907′, opticalswitches 1909 and 1909′, and the optical splitters 1908 and 1908′ areoptically coupled together within the smart port cards 1904A-1904N and1904A′-1904M′ as shown and illustrated in FIGS. 19A and 19B. In eithertype of smart port cards 1904 or 1904′, the optical splitter 1908 or1908′ splits the incoming optical signal into two split optical signalsover two different optical paths one of which is coupled into the firstoptical switch fabric 1910A and the other which is coupled into thesecond optical switch fabric 1910B. In either type of smart port cards1904 or 1904′, the optical switch 1909 and 1909′ selects an opticalsignal from between two optical signals over two differing opticalsignal paths one of which is received from the first optical switchfabric 19010A and the other of which is received from the second opticalswitch fabric 1910B. In this manner should an optical signal path in oneof the two switch fabrics fail for any reason, the optical switch 1909or 1909′ only need select the opposite signal path. For example considerthe exemplary optical path 1915A in the optical switch fabric 1910A andthe optical path 1915A′ in the optical switch fabric 1910B. Splitter1908 in the smart port card 1904A splits an incoming optical signal intotwo split optical signals on optical paths 1921A and 1922A. The signalon the optical path 1921A is coupled into the first optical switchfabric 1910A and the signal on the optical path 1922A is coupled intothe second optical switch fabric 1910B. The optical switches 1910A and1910B switch these optical signals into the exemplary optical signalpaths 1915A and 1915A′ respectively. The optical signal path 1915A inthe optical switch fabric 1910A is coupled into the optical path 1923Nwhich is coupled into the optical switch 1909′ of the smart port card1904N. The optical signal path 1915A′ in the optical switch fabric 1910Bis coupled into the optical path 1924N which is coupled into the opticalswitch 1909′ of the smart port card 1904N. In one case, the opticalswitch 1909′ of the smart port card 1904N selects the optical signalsover the optical path 1915A so that the first optical switch fabric1910A is acting as the active optical switch fabric. In another case,the optical switch 1909′ of the smart port card 1904N selects theoptical signals over the optical path 1915A′ so that the second opticalswitch fabric 1910B is acting as the active optical switch fabric. Ifeither optical switch fabric fails generating a gap, the other isautomatically selected by the smart port cards to bridge the gap.

[0130] In this case, optical signals from the smart port card 1904A arecoupled into the smart port card 1904N such that only one O/E/O 1907 isneeded to regenerate the optical signals input into the opticalcross-connect 1900. If it is desirable to regenerate optical signalsinto as well as out of the optical cross-connect 1900, optical signalsfrom one of the smart port cards 1904A-1904N can be coupled into one ofthe smart port cards 1904A′-1094M′ which have an O/E/O 1907′ toregenerate the output optical signals in the output path.

[0131] Other port cards including passive port cards can be used withmore than one optical switch fabric to provide at least one redundantoptical switch fabric. FIGS. 19B-19G illustrate exemplary embodiments ofother combinations of port cards that can be used with the two opticalswitch fabrics 1910A and 1910B.

[0132] Referring now to FIG. 19B, the optical cross-connect switch 1900Bincludes smart port cards 1804A-1804N, smart port cards 1804A′-1804M′,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric1910B. The elements of smart port cards 1804A-1804N and smart port cards1804A′-1804M′ were previously discussed with reference to FIG. 18. Theoptical cross-connect switch 1900B provides redundancy similar to theoptical cross-connect switch 1900A but uses differing port cards havingdifferent components.

[0133] Referring now to FIG. 19C, the optical cross-connect switch 1900Cincludes smart port cards 1944A-1944N, smart port cards 1944A′-1944M′,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric1910B. Smart port cards 1944A-1944N and smart port cards 1944A′-1944M′utilize optical switches 1928 and 1928′ as opposed to splitters 1908 and1908′ in smart port cards 1904A-1904N and 1904A-1904M′ respectivelywhich were previously described. Optical switches 1928 and 1928′ provideless optical power loss than the splitters 1908 and 1908′ so that astronger optical signal can be routed through the optical switch fabric.

[0134] Referring now to FIG. 19D, the optical cross-connect switch 1900Dincludes smart port cards 1954A-1954N, smart port cards 1954A′-1954M′,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric19101B. Smart port cards 1954A-1954N and smart port cards 1954A′-1954M′utilize optical switches 1928 and 1928′ and optical couplers 1929 and1929′ as opposed to splitters 1908 and 1908′ and optical switches 1909and 1909′ in smart port cards 1904A-1904N and 1904A-1904M′ respectivelywhich were previously described. Optical switches 1928 and 1928′ provideless optical power loss than the splitters 1908 and 1908′. Opticalcouplers 1929 and 1929′ act similar to a multiplexer and can be passiveso that no switching control is required.

[0135] Referring now to FIG. 19E, the optical cross-connect switch 1900Eincludes smart port cards 1954A-1954M, passive port cards 1953A-1953N,test port/monitor card 1905, network management controller (NMC) 1906,first optical switch fabric 1910A, and second optical switch fabric1910B. Smart port cards 1954A-1954M utilize optical switches 1928 andoptical couplers 1929 as opposed to splitters 1908 and optical switches1909 in smart port cards 1904A-1904N respectively which were previouslydescribed. Each of the passive port cards 1953A-1953N include theoptical switch 1928 in the input path and the optical coupler 1929 inthe output path as shown. Each of the passive port cards 1953A-1953N donot have an O/E/O in either their input path or their output path. Thatis, optical cross connect switches providing at least one redundantoptical switch fabric can also use passive port cards to reduce thenumber of O/E/Os and lower costs.

[0136] Referring now to FIG. 19F, alternate combinations of passive portcards and smart port cards can be combined within optical cross connectswitches having at least one redundant optical switch fabric. In FIG.19F, the optical cross-connect switch 1900F includes smart port cards1904A′-1904M′, passive port cards 1963A-1963N, test port/monitor card1905, network management controller (NMC) 1906, first optical switchfabric 1910A, and second optical switch fabric 1910B. Smart port cards1904A′-1904M′ were previously described with respect to FIG. 19A. Eachof the passive port cards 1963A-1963N include an optical splitter 1968in the input path and an optical switch 1969 in the output path asshown. Each of the passive port cards 1963A-1963N do not have an O/E/Oin either their input path or their output path.

[0137] Referring now to FIG. 19G, another embodiment of combinations ofpassive port cards and smart port cards is illustrated for an opticalcross-connect switch having a redundant optical switch fabric. In FIG.19G, the optical cross-connect switch 1900G includes smart port cards1904A′-1904M′, one or more passive port cards 1963, one or more passiveport cards 1503, test port/monitor card 1905, network managementcontroller (NMC) 1906, first optical switch fabric 1910A, and secondoptical switch fabric 19101B. Smart port cards 1904A′-1904M′ werepreviously described with respect to FIG. 19A. Each of the one or morepassive port cards 1963 include an optical splitter 1968 in the inputpath and an optical switch 1969 in the output path as shown, Each of theone or more passive port cards 1503 provides only a flow through opticalpath between input and output ports and the optical switch fabrics. Eachof the passive port cards 1963 and 1503 do not have an O/E/O in eithertheir input path or their output path.

[0138] While its obvious that other combinations of passive port cards,smart port cards, and optical switch fabrics can be formed, it isdesirable to provide optical signal regeneration by routing an opticalsignal over an optical path through the optical cross-connect switch sothat at least one optical-electrical-optical conversion occurs to theoptical signal to increase the optical power level at the output fromwhat was received at the input. The optical-electrical-opticalconversion may used for other reasons as well which were previouslydescribed. If it is desirable, a signaling channel previously describedbetween the optical cross connect switch and attached network or clientequipment can be used to provide information regarding signal conditionsand performance of and around the optical cross-connect switch. Thesignaling channel is particularly desirable if nothing but passive portcards without O/E/Os are used in channels of the optical cross-connectswitch.

[0139] VII. Testing

[0140] The optical cross-connect 1900 having redundant optical switchfabrics can readily provide self testability. The optical cross-connect1900 can optionally include a test port/monitor card 1905 in order totest the optical paths through the first and second optical switchfabrics 1910A and 1910B to perform sophisticated performance monitoringand attach test equipment if needed. One port of either optical switchfabric can be dedicated as a test access port. A test port/monitor cardis inserted into the dedicated test access port. The test port/monitorcard 1905 monitors one of the split signals to determine if there is afailure in the optical path or not as well as to determine performancemeasures for the optical signal including a bit error rate (BER). Anyincoming optical signal passing through the optical cross-connect 1900can be accessed and monitored by switching one of the split signals overto the test access port where the test port/monitor card 1905 ispresent. The other part of the split signal continues to be routedthrough the optical cross-connect 1900 unaffected. The test access portand test port/monitor card 1905 allow non-intrusive monitoring of theincoming optical signals.

[0141] The test port/monitor card 1905 includes an optical switch 1919and an optical to electrical converter (O/E) 1917. The O/E 1917 couplesto a controller within the optical cross-connect 1900 such as the NMC1906 to process the electrical signals from the test port/monitor card1905 representing the optical signal of the tested optical path. Theoptical switch 1917 selects between monitoring an optical path of thefirst optical switch fabric 1910A and an optical path of the secondoptical switch fabric 1910B. The optical switch fabric which is beingmonitored can be referred to as the redundant optical switch fabric,while the optical switch fabric that is being used to carry data overthe communication channel connection is referred to as the activeoptical switch fabric. In FIG. 19A, the second optical switch fabric1910B is being monitored. The test port selects a port to monitor todetermine if an optical signal is actually present on the split opticalpaths and if so, if the optical path carrying the data in the firstoptical switch fabric is reliable or has failed. The signals can also bemonitored to determine what is the bit error rate through the opticalcross-connect switch 1900. The test port card 1905 steps from path topath to sample the signals on the paths to determine where a failure mayoccur. The test port card can use an algorithm such as a round robinalgorithm to test each path in sequence. If a faulty path is detected,the test port card raises an alarm and the information is sent to anetwork management system, for further fault isolation and servicing ofthe failure. The test port 1905 can also ping-pong from one opticalswitch fabric to another in order to alternate the testing process. InFIG. 19A, the second optical switch fabric 1910B is being monitored bythe optical path 1926 using a first test input port. Referringmomentarily to FIG. 20, the first optical switch fabric 1910A is beingmonitored by the optical path 1925 using a second test input port asopposed to the second optical switch fabric 1910B to illustrate theping-pong between optical switch fabrics. Either of the test port cards1905 and 2005 can step from path to path to sample the signals over theoptical paths to determine where a failure may occur. If a faultyoptical path is detected, an alarm is signaled and it is removed fromavailable paths in the respective optical switch fabric until itsrepaired or the redundant optical switch fabric is selected to replacethe failing path.

[0142] Referring now to FIGS. 19A and 20, the test port/monitor card1905 illustrated in FIG. 19A monitors incoming optical signals foreither optical switch fabric. The test port/monitor card 2005illustrated in FIG. 20 can monitor incoming optical signals from eitheroptical switch fabric as well as generate its own optical test signal toactively self-test optical paths through the either optical switchfabric. In addition to the O/E 1917 and the optical switch 1919, thetest port/monitor card 2005 includes an electrical to optical converter(E/O) 1918 (i.e. a semiconductor laser) to generate an optical testsignal which is controlled to actively test optical paths through thefirst and second optical switch fabrics. The test port/monitor cards1905 and 2005 can be used in any configuration of an opticalcross-connect switch including the single and dual optical switch fabricembodiments disclosed herein.

[0143] The present invention is thus described and as one of ordinaryskill can see, it has many advantages over the prior art. One advantageof the present invention is that the costs of regenerating signalswithin an optical cross-connect switch can be reduced by utilizing oneO/E/O in the input path or output path of a smart port card of thepresent invention. Another advantage of the present invention is thatnon-intrusive monitoring can be performed on the incoming opticalsignals using the present invention. Still another advantage of thepresent invention is that self-testing of an optical cross-connectswitch can be performed.

[0144] While certain exemplary embodiments have been described and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of and not restrictive on the broadinvention, and that this invention not be limited to the specificconstructions and arrangements shown and described, since various othermodifications may occur to those ordinarily skilled in the art. Forexample, the present invention has been described in detail using anoptical cross-connect switch. However, the present invention may beimplemented into other optical network equipment that accept opticaldata signals including an optical bridge, an optical router, an opticalhub, an optical node, an optical concentrator, or other networkingequipment accepting a data signal embodied in an optical signal.Additionally, it is possible to implement the present invention or someof its features in hardware, firmware, software or a combination thereofwhere the software is provided in a processor readable storage mediumsuch as a magnetic, optical, or semiconductor storage medium.

1-21. (Cancelled)
 22. A method of regenerating optical signals in anall-optical cross-connect switch, the method comprising: providing oneor more smart port cards, each of the one or more smart port cardsincluding an optical-electrical-optical converter in an optical path,the optical-electrical-optical converter to convert an input opticalsignal into an electrical signal and the electrical signal into anoutput optical signal, the output optical signal being responsive to theinput optical signal; providing one or more passive port cards, the oneor more passive port cards without an optical-electrical-opticalconverter; and generating an optical path through an optical switchfabric of optical switches for optical signals to flow between the oneor more smart port cards and the one or more passive port cards.
 23. Themethod of claim 22 wherein the optical-electrical-optical converter isin the input optical path of each of the one or more smart port cards;and the generating of the optical path through the optical switch fabriccouples the input optical path of the smart port cards to the outputoptical path of the passive port cards.
 24. The method of claim 22wherein the optical-electrical-optical converter is in the outputoptical path of each of the one or more smart port cards; and thegenerating of the optical path through the optical switch fabric couplesthe input optical path of the passive port cards to the output opticalpath of the smart port cards.
 25. The method of claim 22 wherein theoptical-electrical-optical converter monitors the optical signal. 26-93.(Cancelled)
 94. An apparatus for regenerating optical signals in anall-optical cross-connect switch, the apparatus comprising: a smart portcard, the smart port card including an optical-electrical-opticalconverter in an optical path, the optical-electrical-optical converterto convert an input optical signal into an electrical signal and theelectrical signal into an output optical signal.
 95. The apparatus ofclaim 94 wherein the output optical signal is substantially similar tothe input optical signal.
 96. The apparatus of claim 94 wherein theoptical-electrical-optical converter provides wavelength conversion suchthat the output optical signal has substantially similar informationcontent as that of the input optical signal but a differing photonicwavelength.
 97. The apparatus of claim 94 wherein theoptical-electrical-optical converter is in the input optical path of thesmart port card.
 98. The apparatus of claim 94 wherein theoptical-electrical-optical converter is in the output optical path ofthe smart port card.
 99. The apparatus of claim 94 wherein theoptical-electrical-optical converter provides a tap to the electricalsignal to monitor the optical signal.
 100. A method of regeneratingoptical signals in an all-optical cross-connect switch, the methodcomprising: converting a first optical signal into an electrical signal;converting the electrical signal into a second optical signal, thesecond optical signal being responsive to the first optical signal; andforming an optical path through an optical switch fabric of opticalswitches over which optical signals can be transported through theoptical cross-connect switch.
 101. The method of claim 100 wherein theconverting of the first optical signal into the electrical signal andthe converting of the electrical signal into the second optical signalare performed in an input optical path to the all-optical cross-connectswitch.
 102. The method of claim 100 wherein the converting of the firstoptical signal into the electrical signal and the converting of theelectrical signal into the second optical signal are performed in anoutput optical path from the all-optical cross-connect switch.
 103. Themethod of claim 100 wherein the converting of the first optical signalinto the electrical signal and the converting of the electrical signalinto the second optical signal regenerates the first optical signal.104. The method of claim 100 wherein the converting of the first opticalsignal into the electrical signal allows for monitoring of the firstoptical signal.
 105. The method of claim 100 wherein, the first opticalsignal has a first wavelength and the second optical signal has a secondwavelength differing from the first wavelength.